Remote visualization @ UAntwerp#

The UAntwerp clusters have limited features for remote visualization on the login nodes of the clusters and the visualization node of Leibniz using a VNC-based remote display technology. On the regular login nodes of the clusters, there is no acceleration of 3D graphics. However, the visualization node of Leibniz is equipped with a NVIDIA P5000 card that, when used properly, will offer accelerated rendering of OpenGL applications.

Note

Using VNC is a good solution for those who absolutely need a GUI tool or a visualization tool on the cluster rather than on your local desktop. It is not a good solution for those who don’t want to invest in learning Linux properly and are only looking for the ease-of-use of a PC.

Prerequisites#

You’ll need an ssh client on your desktop that provides port forwarding functionality on your desktop. We refer to the Access VSC Infrastructure section for information about ssh clients for various client operating systems. PuTTY (Windows) and OpenSSH (macOS, Linux, UNIX-compatibility environment on Windows) both provide all required functionality.

Furthermore, you’ll need a VNC client. In theory, using the TurboVNC client should result in the least problems, as that is made by the same people as the server we use.

We have tested the setup with four different clients:

  • The TurboVNC client can be downloaded by following the Downloads link on the TurboVNC web site, which will lead you to TurboVNC download page. Binaries are available for both 32-bit and 64-bit Windows systems.

  • TigerVNC is a client whose development is supported by the Swedish company Cendio who makes a remote display server product (ThinLinc) based on TigerVNC. Binaries for 32-bit and 64-bit windows (vncviewer(64)-*.*.*.exe) can be downloaded by following the link on the GitHub Releases page. These binaries are ready-to-run.

  • TightVNC is also a popular free VNC implementation. 32-bit and 64-bit Windows installers can be downloaded from the download page on their website. When installing on your PC or laptop, make sure to choose the “custom install” and only install the TightVNC Viewer.

  • MobaXterm also has an integrated VNC viewer. With that viewer it is possible to build the tunnel in the network settings of the VNC connection.

All four viewers are quite fast and offer good performance, even when run from home over a typical broadband internet connection. TigerVNC seems to be a bit quicker than the others, while TightVNC and MobaXterm don’t allow you to resize your window. With the other two implementations, when you resize your desktop window, the desktop is also properly resized.

Here also there are several possible setups:

  • The TurboVNC client can be downloaded from the TurboVNC web site. The macOS client is Java-based. It requires Oracle Java (which you will need to install if it is not yet on your system).

  • TigerVNC, a client whose development is supported by the Swedish company Cendio who makes a remote display server product (ThinLinc) based on TigerVNC, is a native macOS client. Some places report that this client is a lot slower than the TurboVNC one on macOS. Binaries are available by following the link on the GitHub Releases page. Look for the tigervnc-*.dmg files, which contrary to those for Windows and Linux, only contain the viewer software.

  • A not-so-good alternative is to use the Apple Screen Sharing feature which is available through Finder (Command-K key combination) or Safari (URL bar) by specifying the server as a URL starting with vnc://. The port number is 5900 + the number of the VNC server if you follow the scheme below to start an application in a VNC session. For example, with port tunnelling and a VNC server with number 2, the server address will be vnc://localhost:5902. This VNC client is considerably slower though than the TurboVNC client, partly because it doesn’t support some of the TurboVNC-specific compression algorithms.

RPM and Debian packages for TurboVNC can be downloaded from the TurboVNC web site and are available in some Linux distributions. You can also try another VNC client provided by your Linux distribution, although we cannot guarantee those will work with our TurboVNC server.

How do I run an application with TurboVNC?#

Running an application with TurboVNC requires 3 steps:

  1. Start the VNC server on the cluster

  2. Start the VNC client on your desktop/laptop and connect to the server

  3. Start your application

Step 1: Starting the VNC server#

  1. Log on in the regular way to one of the regular login nodes or to the visualization node of Leibniz. Note that the latter should only be used for running demanding visualizations that benefit from the 3D acceleration. The node is not meant for those who just want to run some lightweight 2D GUI application, e.g., an editor with GUI.

  2. Load the module vsc-vnc:

    module load vsc-vnc

  3. Use the wrapper script to start the VNC server and the Xfce desktop environment:

    vnc-xfce

  4. The first time you use VNC, it will ask you to create a password.

    Note

    For security reasons, please use a password that you don’t use for anything else. If you have forgotten your password, it can easily be changed with the vncpasswd command and is stored in the file ~/.vnc/passwd in encrypted form. It will also ask you for a viewer-only password. If you don’t know what this is, you don’t need it.

  5. Among other information, the VNC server will show a line similar to:

    Desktop 'TurboVNC: viz1.leibniz:2 (vsc20XXX)' started on display viz1.leibniz:2

    Note the number after TurboVNC: viz1.leibniz, in this case 2. This is the number of your VNC server, and it will in general be the same as the X display number which is the last number on the line. You’ll need that number to connect to the VNC server.

  6. Optional It is now safe to log out from your SSH session. The VNC server will continue running in the background.

Step 2: Connecting to the server#

In most cases, you will not be able to connect directly to the TurboVNC server. Instead, you will need to create an SSH tunnel to forward traffic to the VNC server. The exact procedure is explained at length in the pages “Creating a SSH tunnel using PuTTY” (for Windows) and “Creating a SSH tunnel using OpenSSH” (for Linux and macOS).

In the following example, we assume the VNC server was started with number 2, running on port 5902 (VNC’s default port 5900 + your server number).

  1. First, setup an SSH tunnel.

    In theory, you can create an SSH tunnel from any port number on your local machine to the port number on the node running the VNC server. However, it is easier to use the same port number on both ends of the tunnel.

    Warning

    Avoid using the generic login names here, as that may result in an SSH tunnel to a different login node as the one running your VNC server. Instead, use the full names for the specific nodes, e.g., viz1-leibniz.hpc.uantwerpen.be, login2-leibniz.hpc.uantwerpen.be or login1-vaughan.hpc.uantwerpen.be.

    For a VNC server started with number 2 on the visualization node, your command will look like

    ssh -L 5902:localhost:5902 -N [email protected]

    The above line assumes that you log on to the node where the VNC server is running, which is why we can use localhost in the -L-line (as this is the name under which the node running the VNC server is known on that node).

    Select "Connections - SSH - Tunnel" in the left pane. As "Source port", use 5900 + the server number (5902 in our example). As destination, use the full name of the node on which the VNC server is running, e.g., viz1-leibniz.hpc.uantwerpen.be, or localhost if you will log on to the node running the VNC server.

  2. Start your VNC client once your tunnel is up-and-running. The procedure depends on the precise client you are using.

    In general, the client will ask for the VNC server address. The server address is localhost:x where x is the number of your VNC server (2 in the example above). Some clients also allow you to use the port number instead (localhost:5902 for the example above), and will automatically assume that bigger numbers are port numbers.

    The client will then ask you for the password that you have assigned when you first started a VNC server.

  3. You should now get a window with the desktop environment that you have chosen when starting the VNC server

    Note

    The first time that you start a Xfce session with TurboVNC, you’ll see a panel “Welcome to the first start of the panel”. You may want to select “Use default config”, as otherwise you get a very empty desktop.

Step 3: Starting an application#

  1. Open a terminal window in the VNC session. In the default Xfce-environment, you can open a terminal window by selecting "Terminal Emulator" in the "Applications" menu in the top left. The first time it will let you choose between selected terminal applications.

  2. Load the modules that are required to start your application of choice.

  3. 2D applications or applications that use a software renderer for 3D start as usual. However, to start an application using the hardware-accelerated OpenGL, you’ll need to start it through vglrun. This will use VirtualGL to redirect the OpenGL calls to your VNC server’s display.

    Adding vglrun at the start of the command line is usually sufficient.

    Note

    For a quick test of your setup, enter

    vglrun glxinfo
vglrun glxgears

    The first command will print some information about the OpenGL functionality that is supported. The second command will display a set of rotating gears. Don’t be fooled if they appear to stand still but look at the "frames per second" printed in the terminal window.

    However, this doesn’t work with all applications. Some applications, like MATLAB, might require a special setup.

    Example Start MATLAB with hardware-accelerated OpenGL with -nosoftwareopengl as follows:

    vglrun matlab -nosoftwareopengl

    The MATLAB command opengl info will then show that you are indeed using the GPU.

  4. When you’ve finished, don’t forget to log out in the Xfce desktop (right mouse click in the desktop, then select "Application" and then select "Log Out") when you use one of our wrapper scripts or kill the VNC server otherwise using

    vncserver -kill :x

    with x the number of the server.

Warning

Do not forget to close your tunnel when you log out from the VNC server. Otherwise the next user might not be able to connect.

Common problems#

  • Authentication fails when connecting to the server

    This happens occasionally when switching between different versions of TurboVNC. The easiest solution is to simply kill the VNC server using vncserver -kill :x (with x the display number), set a new VNC password using vncpasswd and start over again.

  • Xfce doesn’t show the task bar at the top of the screen

    This sometimes happens when switching between versions of Xfce4, or you may have screwed up your configuration in another way. Remove the .config/xfce-centos7 directory (rm -r .config/xfce-centos7), kill the VNC server and start again.